The following internal Ministry of Transportation of Ontario (MTO) memorandum dated June 2009 explains why concrete pipe was solely specified for culverts under Highway 69 near Sudbury, Ontario, and why High-Density Polyethylene (HDPE) pipe and corrugated steel pipe (CSP) were not allowed. The memorandum was obtained under The Freedom of Information and Protection of Privacy Act. The memorandum clearly points to concrete pipe being the most reliable, safest and cost effective compared to HDPE and CSP.
The culverts listed in the table below (table omitted here for brevity) are
recommended as concrete only because of the risks and impact of prematur failure. Section 9.3 “Summary of Risk Factors for alternative Pipe Types” of the Ministry of Transportation Gravity Pipe Design Guidelines summarizes risk factors that may need to be considered in the selection of the most suitable pipes for a particular application.
One of the factors to consider is the repair costs and mitigation measures as a result of improper installation or premature failure.
The seventeen culverts listed above are situated on the mainline of Highway 69 (future 400) /Highway 637 interchange ramps/Highway 637 and are in areas of rockfill embankment where the depth from the top of pavement to pipe invert is in excess of 3m. Repair costs and mitigation measures as a result of improper installation and/or premature failure for these culverts are significant. Future replacement of these culverts would require full road closures or the construction of expensive detours. Full road closures on Highway 69 in this area would severely inconvenience and compromise the safety to the traveling public.
No research has been undertaken to establish criteria for establishing
the EMSL for HDPE pipe for highway applications in Ontario. The ministry accepts an assumed EMSL of 75 years for HDPE pipe for RSC 250. However, where the application requires a DSL of 75 years, post-installation verification of the pipe integrity should be undertaken, such as by mandrel pull or video inspection and it should be verified that there are no unusual risk factors associated with the application. While Post-Installation Inspection will be performed as per SP 104S02, only 25 per cent of the pipes will be inspected.
For Polymer Laminated (PL) & Aluminized Type 2 Coated Steel
Pipe (ALT2) – coated pipes:
The risk of premature pipe failure as a result of damage during the installation of a culvert in a rockfill embankment is significant for coated steel pipes. Damage to the coating will compromise its effectiveness; consequently, the estimated material service life for these culverts cannot accurately be determined.
“Therefore, only concrete culverts are acceptable at these locations because of the nature of the risk, the probability of occurrence, and most importantly, the consequences of premature failure.”
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